App crashes in Release build but not in debug

Question

As I said in the title, I am writing an app for iPhone which runs perfectly in debug mode but when I build it as release and install it via TestFlight, it crashes. Due to the crash log it might have to do something with this lines:

let path = NSBundle.mainBundle().pathForResource("PrinterList", ofType: "plist")
if path != nil {
    let printerDic = NSDictionary(contentsOfFile: path!)
    let printerList = NSArray(array: printerDic.allKeys)
    printerNames = printerList as [String]
}

I am using an framework from Brother to print without AirPrint, but I think thats not the problem because the app crashes before doing something with the framework. It crashes only in this ViewController where I execute these lines. I need the framework only in this ViewController as well.

Answer 1

There are many reasons that an app might crash in release mode but not in debug mode (e.g. memory allocation differences showing up a bug that actually exists in both builds.) They can take a lot of work to track down, even with a non-beta compiler/language.

You say that the problem goes away if you do as I suggested and build for release with optimisations turned off. Given that the Swift compiler is still in beta and definitely still has the occasional problem—I've seen the compiler simply crash when building optimised builds—this may actually be an optimiser bug.

For now, therefore, I'd defer looking into it. Release without optimisations until we get a full release version of the compiler. Then, turn optimisations back on and see if you still have the problem. If you do, that's the time to start spending your energy trying to figure out if it's a compiler bug or a bug in your own code.